During the servicing and maintenance of turbine engines, in order to minimize down time, it is often desirable to quickly determine the general condition of the turbine and to find problem areas as soon as it is opened. This requires an ability to quickly access internal components and to conveniently obtain and accurately record a number of precise measurements of component clearances. For example, upon removal of the top half of a turbine rotor housing, it may be necessary to measure opening clearances between two surfaces such as: (1) wheel clearances between the turbine rotor and housing; (2) rotor position checks; (3) thrust clearances; and (4) gib key clearances. Such measurements are often indicative of the general condition of a turbine and provide needed information for the proper diagnosis of potential problem areas. Since turbine downtime is often costly to the customer, it is imperative that such measurements be taken as quickly and accurately as possible, particularly in those cases where the rotor is to be removed from the housing. Likewise, when closing the turbine housing, it is again important to take measurements quickly and accurately so as to insure that the reinstalled rotor is correctly and accurately located.
In the past, these measurements were taken with various types of taper gauges and parallel gauges which proved time consuming to use and difficult to read. For example, in order to obtain measurements to the desired degree of accuracy, a conventional taper gauge must be relatively long and have a very slim taper (i.e., a small slope) to obtain readings. This often causes a problem with "bottoming out", particularly at the tip of the rotor where a taper gauge inserted to measure a radial clearance will interfere with the housing. In order to overcome this problem it would be possible to use a number of different-sized shorter and truncated tapers. Alternatively, a curved taper gauge could be manufactured to conform to the radius of the turbine to avoid interference with the housing. However, curved gauges are very expensive and the other alternative of using numerous shorter sized truncated tapers is time consuming and cumbersome.
Moreover, for larger openings or clearances, a "parallel" gauge is often required. This type of gauge requires insertion of the gauge into the opening and then extending the parallel gauge surfaces until contact is made. The gauge is then locked and carefully withdrawn so that the distance between its parallel surfaces may be measured with a micrometer. Obviously, this is a time-consuming and error-prone process. As a result and due to these problems, maintenance personnel often forego taking many crucial and useful measurements.
In accordance with a preferred exemplary embodiment of the invention, the digital taper/parallel gauge includes a flat wedge-shaped taper block in combination with a commercially available linear scaling device incorporating a digital scale display unit mounted on one side of the taper block, a scale slider having one end modified to provide a series of tapered steps, and a slide stop piece attached to the opposite end of the scale slider. To measure a particular clearance, the gauge is inserted into the opening or gap until the taper block fills the space. In doing so, the scale slider is displaced with respect to the taper block and scale display unit assembly by the amount the taper block is inserted. The amount of scale slider travel is measured and an indication is provided on the scale display unit.
Moreover, since the amount o scale slider travel (i.e., the displacement of the slider when the gauge is inserted into the opening) is directly related to the clearance at that point (i.e., it is a linear function directly related to the slope of the taper), the taper block can be designed with almost any selected desired conversion factor incorporated into the slope of the taper block wedge enabling the scale display unit to provide read-out conversions between differing units of measurement directly. In addition, the tapered step surfaces at one end of the scale slider are sloped in the opposite direction as the slope of the taper block so that the top surfaces of the steps are parallel with the bottom edge of the taper block. This arrangement serves to provide multiple sets of parallel surfaces that may be used to extend the useful measurement range of the gauge. Essentially, the tapered steps effectively provide measuring surfaces of selectable starting thicknesses so as to allow use of gauge where a longer taper block would otherwise "bottom out" or impinge on some internal obstruction before the tapered wedge portion of the block fills the gap. A slide-stop piece is also fitted at the opposite end of the scale slider to act as an end stop and a zero reference point.
In an alternative embodiment, the scale display unit and slider are mounted orthogonal to the sides of the taper block along its sloped edge. An interchangeable end-slide piece is removably attached at one end of the scale slider and functions as one-half of a set of parallel measuring surfaces (the other half being the bottom edge of the taper block) as well as a stop for the taper gauge. The end slide piece is likewise provided with stepped tapered surfaces of the same slope, albeit in the opposite direction, as that of the taper block. Several end-slide variations containing none, one or more steps are contemplated to accommodate a variety of measurement ranges.
More specifically, accordance with a preferred exemplary embodiment of the invention, a digital taper/parallel gauge tool comprises a wedge-shaped (taper block) body portion having a sloped edge and a bottom edge, a digital scale display unit fixedly secured to said taper block, a movable scale slider portion operatively associated with said digital scale unit, said scale slider capable of translational displacement along said sloped edge of the taper block, said scale slider having at least one tapered edge surface of the same slope but opposite direction as that of said sloped edge of said taper block such that said tapered edge of the slider and said bottom edge of the taper block form parallel surfaces of variable separation, and said digital scale unit measuring the amount of translational displacement of said scale slider with respect to said taper block and displaying an indication of the orthogonal distance between said bottom edge and said sloped edge of the taper block at a position determined by one end of said scale slider.
It is, therefore, a principal object of this invention to make turbine rotor clearance measurements more easily, accurately and quickly. It is also another object of this invention to provide a combination taper/parallel gauge capable of measuring a large range of opening clearances. It is also a further object of this invention to provide an inexpensive, accurate and ergonomic gauge tool for measuring opening clearances in turbine engines. Other objects and advantages of the invention will become apparent from the detailed description which follows .